It’s been a puzzle for a while: Why aren’t companies responding to historically low interest rates by ramping up corporate investment?

It’s because low interest rates don’t really spur corporate investment, according to new research. The paper from S.P. Kothari of MIT, Jonathan Lewellen of Dartmouth and Jerold Warner of the University of Rochester was last updated in March and published this weekend in an article by the MIT Sloan School of Management.

What did spur companies to invest were two things: profits and stock prices. For every dollar rise in profits, investment goes up 25 cents in the following quarter and nearly a dollar in five quarters. Stock-market moves aren’t quite as strong, but a 10% rise in stock prices leads to a 4% rise in investment over 18 months.

Intriguingly, the drop in corporate investment after the Great Recession doesn’t seem to be the result of a drying-up of lending but rather of tumbling GDP, corporate profits and stock prices.

The research also suggests that executives invest cyclically instead of countercyclically. “High investment growth appears to be bad news, suggesting that it is poorly timed and wasteful. The investment response to prior profits may reflect, in part, an overreaction to good performance that does not persist,” the researchers say.

As for policy makers, Kothari says in the MIT article that they should focus on tax rates, regulation and labor policy, since those are the factors that drive investment.